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The community and team of scientists that help NASA prioritize space missions has come out with its exploration recommendations for the next decade: get to Mars, explore one of Jupiter's moons and study Uranus.

"Our recommendations are science-driven, and they offer a balanced mix of missions -- large, medium, and small -- that have the potential to greatly expand our knowledge of the solar system," said Steven Squyres, professor of astronomy at the Center for Radiophysics and Space Research, Cornell University, and chair of the committee that wrote the report. "However, in these tough economic times, some difficult choices may have to be made. With that in mind, our priority missions were carefully selected based on their potential to yield the most scientific benefit per dollar spent."

However, if NASA's budget over that decade cannot support all of these missions, the agency should preserve smaller scale missions in its New Frontiers and Discovery programs first and delay some or all of the recommended large-scale missions, the report says.

To come up with the list, the scientists gathered input from the planetary sciences community as well as NASA and its budget predictions for 2013-2022. An independent contractor also provided cost and technical analyses of select mission proposals.

The priorities in order were:

Roll out the Mars Astrobiology Explorer Cacher (MAX-C): This mission "could help determine whether the planet ever supported life and could also help answer questions about its geologic and climatic history should be NASA's highest priority large mission, the report says. This mission will be the first step in a multipart effort to eventually return samples from the planet. The report stresses, however, that the mission should be conducted only if the cost to NASA is approximately $2.5 billion -- $1 billion less than the independent estimates provided to the committee. NASA and the European Space Agency, which would run the mission jointly, should work together to reduce the scope of the mission and ensure that both agencies still benefit.

"Mars is unique among the planets in having experienced processes comparable to those on Earth during its formation and evolution. Crucially, the Martian surface preserves a record of earliest solar system history, on a planet with conditions that may have been similar to those on Earth when life emerged. It is now possible to select a site on Mars from which to collect samples that will address the question of whether the planet was ever an abode of life. The rocks from Mars that we have on Earth in the form of meteorites cannot provide an answer to this question. They are igneous rocks, whereas recent spacecraft observations have shown the occurrence on Mars of chemical sedimentary rocks of aqueous origin, and rocks that have been aqueously altered. It is these materials, none of which are found in meteorites, that provide the opportunity to study aqueous environments, potential prebiotic chemistry, and perhaps, the remains of early Martian life," the report states.

Explore Jupiter's icy moon Europa: The scientists said this mission to explore Europa and its subsurface ocean offer "one of the most promising environments in the solar system for supporting life -- should be the second priority for NASA's large-scale planetary science missions. However, NASA should fly the Jupiter Europa Orbiter (JEO) only if NASA's budget for planetary science is increased, the report says, and JEO's mission scope is made more affordable. The independent estimate put the price tag at $4.7 billion.

"This moon, with its probable vast subsurface ocean sandwiched between a potentially active silicate interior and a highly dynamic surface ice shell, offers one of the most promising extraterrestrial habitable environments in our solar system and a plausible model for habitable environments outside it. The Jupiter system in which Europa resides hosts an astonishing diversity of phenomena, illuminating fundamental planetary processes. While Voyager and Galileo taught us much about Europa and the Jupiter system, the relatively primitive instrumentation of those missions, and the low data volumes returned, left many questions unanswered. Major discoveries surely remain to be made," the report states.

Fly to Uranus: At a cost of about $2.7 billion the mission to fly a Uranus Orbiter and Probe mission to investigate that planet's interior structure, atmosphere, and composition gets third priority position. The report says that this mission should be initiated between 2013 and 2022, but it should be subjected to rigorous, independent cost verification and cancelled if costs grow significantly above its assessed price tag.

"The gas giants Jupiter and Saturn have been extensively studied by the Galileo and Cassini missions, respectively. But Uranus and Neptune represent a wholly distinct class of planet. While Jupiter and Saturn are made mostly of hydrogen, Uranus and Neptune have much smaller hydrogen envelopes. The bulk composition of these planets is dominated instead by heavier elements; oxygen, carbon, nitrogen, and sulfur are the likely candidates. What little we know about the internal structure and composition of these "ice giant" planets comes from the brief flybys of Voyager 2. So the ice giants are one of the great remaining unknowns in the solar system: the only class of planet that has never been explored in detail. The proposed program will fill this gap in our knowledge by initiating a mission to orbit Uranus and put a probe into the planet's atmosphere. It is exploration in the truest sense, with the same potential for new discoveries as Galileo at Jupiter and Cassini at Saturn," the report states.

Other smaller, non-specific missions were recommended by the group as well. For example, Scientists recommended that NASA select two new missions to be included in its New Frontiers program, which explores the solar system with frequent, mid-size spacecraft missions. The committee recommended that NASA also select a fourth and fifth mission in the 2013-2023 time frame.

From the report: "These New Frontiers candidates cover a vast sweep of exciting planetary science questions: The surface composition of Venus, the internal structure of the Moon, the composition of the lunar mantle, the nature of Trojan asteroids, the composition of comet nuclei, the geophysics of Jupiter's volcanic moon Io, and the structure and detailed composition of Saturn's atmosphere. And continuation of the highly successful Discovery program, which involves regular competitive selections, will provide a steady stream of scientific discoveries from small missions that draw on the full creativity of the science community."

Cooney is an Online News Editor and the author of the Layer 8 blog, Network World's daily home for the not-just-networking news. He has been working with Network World since 1992. You can reach him at mcooney@nww.com.